Question 23.2

Causes of a flat capnograph trace

Outline four causes for the below capnograph trace (Figure 23.3) obtained from a critically ill patient.
(20% marks)

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College answer

Not available.


Because "(Image removed from exam report.)", and because this abomination of a paper was published without official answers, we have no idea which exact ventilator loop the college chose for this. However, it is possible to guess, on the basis of the fact that the wording of this question is identical to the wording of Question 13.2 from the first paper of 2014.

Reasons for a flat or nearly flat CO2 trace include the following:

  • The patient is dead
  • Cardiac / respiratory arrest
  • Apnoea test in a brain dead patient
  • Oesophageal intubation has occurred
  • Ventilator disconnection
  • Airway obstruction (eg. patient suddenly bit down on the tube)
  • ETT perforation (the end tidal gas is escaping via the hole before it gets to the capnograph)
  • Capnograph disconnection or obstruction
  • Water droplet contamination of capnography module